SSL 4000 master bus headroom and signal routing questions

[atticmike]

Howdy fellas,

I embarked on the journey of  better understanding the SSL's signal flow and how it interacts with each headroom instance up until the master bus. So far, my progress has been excellent, granted I already knew lots of stuff by fixing the desk myself.

Now, two things I couldn't make out so far are the master buss's headroom in decibels (technically, it should be as of all cards around 26 dbU - +/- 18V, 36V pp, 12.78 V RMS, dBu 24.34) and whether an overloading channel (on purpose) maxing out internally still hits the master full scale at 26 dbU or gets trimmed down according to the max 16 dBu plasma meter.

Any support of this community would be highly appreciated 

 

[PRR]

> +/- 18V, 36V pp, 12.78 V RMS

You always have some losses. A very good power-amp can't hardly pull to 2V of the total supply, so 34V p-p. Nicer amps may lose 2V-3V each side, maybe barely 30V p-p.

Not a big difference, but if you must compute dB to 2 decimal places you should be realistic.

> whether an overloading channel (on purpose) maxing out internally still hits the master full scale at 26 dbU or gets trimmed down according to the max 16 dBu plasma meter.

I never drooled in an SSL, but basic thinking......

Meters don't usually tell their sources what to do. I set my multi-meter to 100V, poke a 125V wall outlet. The meter says "OVER" (or smokes), but the wall is still 125V.

I would *assume* that after your meter top light lights, you can turn-up another 6dB or 7dB without clipping. Yes, you don't know when clipping will start. It only tells you that if the top lamp is not lit (or hardly-ever lit), you don't have clipping yet.

If you must slam this fine machine, and need the meter to tell you your slamming, put a 10dB or 12dB pad in front of the meter input.

 

[atticmike]

> +/- 18V, 36V pp, 12.78 V RMS

You always have some losses. A very good power-amp can't hardly pull to 2V of the total supply, so 34V p-p. Nicer amps may lose 2V-3V each side, maybe barely 30V p-p.

Not a big difference, but if you must compute dB to 2 decimal places you should be realistic.

> whether an overloading channel (on purpose) maxing out internally still hits the master full scale at 26 dbU or gets trimmed down according to the max 16 dBu plasma meter.

I never drooled in an SSL, but basic thinking......

Meters don't usually tell their sources what to do. I set my multi-meter to 100V, poke a 125V wall outlet. The meter says "OVER" (or smokes), but the wall is still 125V.

I would *assume* that after your meter top light lights, you can turn-up another 6dB or 7dB without clipping. Yes, you don't know when clipping will start. It only tells you that if the top lamp is not lit (or hardly-ever lit), you don't have clipping yet.

If you must slam this fine machine, and need the meter to tell you your slamming, put a 10dB or 12dB pad in front of the meter input.

I agree with everything you've just said but it'd like to hear someone who knows his way around the 4k guts.

And yeah, that's pretty much the same way I've been thinking about it, the meter slamming around the same area once this point's been crossed.

About the power amp theory, i just kept it as theoretical and straight as possible and know it's not all bread and butter.

Thanks for your encouraging words though

 

[radardoug]

So do you have access to a 4000 or is this all theoretical? I note you are posting on another forum and I answered you there.
I have been in the guts of a 4000 and undneath it as well. My previous suggestions still apply. If you have access to a 4000, get a millivoltmeter and a scope and measure it. I'm sure SSL set up the meter to give meaningfull readings with the following recording device that was attached to it, usually a tape recorder in the early days. The transition to digital has meant that metering has somewhat changed, in that digital full scale is now an absolute point of no return. In tape days, you could push the tape hard if you wanted to or not.

 

[atticmike]

So do you have access to a 4000 or is this all theoretical? I note you are posting on another forum and I answered you there.
I have been in the guts of a 4000 and undneath it as well. My previous suggestions still apply. If you have access to a 4000, get a millivoltmeter and a scope and measure it. I'm sure SSL set up the meter to give meaningfull readings with the following recording device that was attached to it, usually a tape recorder in the early days. The transition to digital has meant that metering has somewhat changed, in that digital full scale is now an absolute point of no return. In tape days, you could push the tape hard if you wanted to or not.

Yes I do have a desk at my studio but don't know at which point i'd have to measure it, considering the VCA fader out and other things.

I wanna go  hybrid and recreate what I've been used to mix into.

I'm good at fixing the console / cards but have a hard time understanding the routing / headroom whereabouts, in terms of how overloading channels interact with the master bus / respond to the meter bar.

 

[radardoug]

You should run the master fader full up and trim your channel levels to ensure your mix peaks to zero. The master fader is for doing fades. If you really want to check overload levels, record a track of 1 kHz at zero in your recording device and copy it to say 24 channels. Then feed those 24 channels into the mixer and see what output level you get. Any distortion in the master section will be very obvious with this test.
The use of VCA's is another way of optimising levels.

 

[Andy Millar]

Hi Mike,

Saw your PM (once I'd remembered how to get back into the forum!), hopefully you've seen mine.

The gain is 0dB throughout the mix system so you're right, if the fader is set to unity and the pan is hard over one way then clipping the channel basically will clip the quad bus mixers too. With the pan central each bus will be (IIRC) 4.5 dB down giving you some extra headroom (sort of).

Hope this helps, anyway I've put contact details in my PM and happy to help out in more detail if I can - as much as my fading memory allows!

Cheers,

Andy